Recharging an embedded battery in a smart card

ABSTRACT

Devices and methods for recharging an embedded battery in a smart card, including a control method implemented by a smart card (CD1) including a rechargeable battery (8). The control method may include operations for processing a transaction (TR1) with a terminal (T); receiving during this transaction a predetermined transaction command requiring a processing time, by the smart card, long enough to allow a recharging of the battery to at least a first predetermined threshold charge level; and, upon detection (S32) of this transaction command, triggering the recharging of the battery (8) by using a power supply delivered by the terminal (T) to reach at least the first predetermined threshold charge level.

BACKGROUND OF THE INVENTION

The present invention lies in the general field of smart cards andrelates more particularly to the electrical recharging of smart cardsincluding a battery.

The invention applies more particularly, but not exclusively, to thesmart cards in accordance with the ISO 7816 standard. The invention aimsin particular to the recharging of a battery embedded in a smart cardoperating according to the EMV (Europay Mastercard Visa) protocol,although other protocols are possible as explained later.

Generally, a smart card is designed to communicate with a deviceexternal to this card, otherwise called terminal or reader. The smartcards make it possible to carry out various types of transactions suchas, for example, payment, direct debit or holder authenticationtransactions. The smart cards for banking applications (credit card,debit card etc.), for example, are able to cooperate with paymentterminals or automated teller machines (ATM) to carry out variousfinancial operations.

To carry out a transaction, the smart card holder generally must insertthe card in a reader (contact mode) or, where necessary, may present hiscard in the vicinity of the reader in order to establish a contactlesscommunication with the reader (contactless mode).

In known manner, a smart card includes an electronic chip embedded in acard body. If the smart card is intended to communicate by contact witha reader, it has external contacts disposed on the surface of the cardbody and configured to cooperate by contact with a reader provided forthis purpose. Furthermore, if the smart card is intended to communicatewithout contact with a reader, it embeds in particular a radio frequency(RF) antenna to exchange RF signals with the reader.

More recently, new smart cards have emerged, these can embed variouscomponents more or less complex allowing the implementation ofadditional features. Some smart cards embed for example a screen, anindicator light, a button or a biometric sensor.

Such embedded components in a smart card, however, require a significantpower supply to be able to operate. The growing resources and capacitiesof the smart cards are therefore accompanied by a significant increasein their power consumption.

To this end, these smart cards can also embed a cell serving as aninternal power supply source, but the use of a cell is not alwaysadapted insofar as it is generally not possible to recharge it, whichconsequently limits the lifetime of the smart card.

To meet the growing needs in terms of power supply, it is also known tointegrate a rechargeable battery in a smart card. It has been found,however, that the recharging of such a rechargeable battery in a smartcard is generally not managed in a satisfactory manner, which limits theefficiency of the battery and reduces its lifetime.

There is therefore a need for a solution for electrically powering in aneffective manner at least one embedded electronic component in a smartcard. Particularly, there is a need to recharge effectively a batteryembedded in a smart card in order in particular to optimize theperformances of the battery, and consequently, of the smart card.

OBJECT AND SUMMARY OF THE INVENTION

As indicated above, the management of the power supply in the smartcards embedding an internal battery is not satisfactory today. Theincrease in the complexity of the smart cards, and particularly theintegration of more and more numerous and complex components (sensors,screens . . . ), lead to a significant increase in the power consumptionin these cards.

The significant technical constraints, in particular with regard to thereduced space available in smart cards, make the management of theembedded batteries even more complicated.

In the life of a battery, the latter experiences alternation of rechargephases and discharge phases.

FIG. 1 schematically illustrates a graph GP, representing the chargelevel NC of a battery over time in one particular example, this batterybeing for example embedded in a smart card.

In this document, the charge level NC of a battery is defined inpercentage (%) with respect to the total charge level it canintrinsically withstand.

As represented in FIG. 1, at a given instant t, the battery isinherently discharged over time and must therefore be rechargedregularly to maintain a sufficient charge level NC to allow a normal useof the smart card. Over time, the charge level NC passes through aseries of cycles CL, called “recharge cycles” or “recharge/dischargecycles”, each of these cycles being defined by two consecutive phases,namely: a recharge phase and a discharge phase. As indicated later, therecharge and discharge phases of a cycle are not necessarily complete. Arecharge cycle can have various charge level NC amplitudes (maximumamplitude: from 0 to 100%).

The change in the charge level NC depends on various factors includingin particular: the characteristics of the battery, its environment, itsuse . . . During a recharge phase, the battery undertakes an energycollection process for increasing the charge level NC, the change in thecharge level NC, dependent particularly on the recharge time and on thepower supply provided to the battery.

In the example represented in FIG. 1, the battery is thus subjected to 4successive recharge cycles CL1-CL4:

-   -   Cycle CL1 (between t0 and t2): the battery experiences a        recharge phase between the times t0 and t1 increasing its charge        level NC by 60%, then a discharge phase between t1 and t2;    -   Cycle CL2 (between t2 and t4): the battery experiences a        recharge phase between the times t2 and t3 increasing its charge        level NC by 50%, then a discharge phase between t3 and t4;    -   Cycle CL3 (between t4 and t6): the battery experiences a short        recharge phase between the times t4 and t5 and then a discharge        phase between t5 and t6: and    -   Cycle CL4 (between t6 and t8): the battery experiences again a        short recharge phase between the times t6 and t7 and a discharge        phase between t7 and t8.

The configuration of each recharge cycle CL (the peak shape representingthe change in the charge level NC) may vary depending on the case. It iscommon for a battery not to reach its maximum charge level NC during arecharge phase. Similarly, the complete depletion of a battery isgenerally avoided during a discharge phase.

As represented in FIG. 1, micro-recharging operations such as thosecarried out during the cycles CL3 and CL4 are possible, during which avery small increase (of 0.5 or 1%, for example) in the charge level NCof the battery is achieved. This phenomenon of micro-recharging can havevarious origins.

However, it has been observed that such micro-recharging operations haveindeed a detrimental effect on the performances of a battery, and inparticular a battery embedded in a smart card. The batteries are alsogenerally capable of withstanding a limited number of recharge cyclesduring their lifetime (this number ranging for example between 300 and500 recharge cycles). Once this critical number of cycles is reached,the performances of the battery, and particularly the battery life,decrease substantially.

To effectively recharge a battery embedded in a smart card, it has beenobserved that it is necessary to deliver a stable power supply for asufficient period of time to allow the battery to reach a predeterminedthreshold charge level (which can be below or equal to its nominalcapacity). Particularly, the power supply must not be interrupted earlybefore reaching this threshold charge level, which then allows ensuringthe supply of the smart card without external energy source to performone or several operations (financial transaction, authentication,Bluetooth communication, display of a dynamic cryptogram . . . ).

It has been envisaged to recharge the internal battery of a smart cardby using an external terminal with which the smart card cooperates bycontact to process an EMV-type transaction or the like. However, therecharging of the battery is not always satisfactory because it isdifficult to ensure a stable supply of the battery by the externalterminal. Indeed, during an EMV transaction for example, the exchangesbetween the external terminal (the reader) and the smart card are veryvariable and are subject to fluctuations or interruptions during therecharging process of the battery. Thus, during certain processingoperations carried out by a smart card during an EMV transaction(including cryptographic processing operations), the power consumptionof the smart card can increase considerably, thus limiting the powersupply that remains available to recharge the embedded battery.

The instability of the supply, and more particularly the interruption ofa recharge phase, degrade the results in terms of recharging andaccelerate the aging of the battery, thus reducing its lifetime.

The invention therefore aims at improving the management of theelectrical recharging of a battery embedded in a smart card, taking intoaccount in particular the constraints and observations indicated above.

To this end, the present invention relates to a control methodimplemented by a smart card including a rechargeable battery, the methodcomprising:

-   -   processing a transaction during which the smart card        communicates with an external terminal with which said smart        card is coupled;    -   receiving, during said processing of the transaction, a        predetermined transaction command requiring a processing time,        by said smart card, long enough to allow a recharging of the        battery to at least a first predetermined threshold charge        level; and    -   upon detection of said predetermined transaction command,        triggering the recharging of the battery by using a power supply        delivered by the external terminal to reach at least the first        predetermined threshold charge level.

The invention makes it possible to implement an intelligent electricalrecharging of the battery, as explained below.

According to one particular embodiment, the first predeterminedthreshold charge level corresponds to at least 50% of the maximum chargecapacity of the battery. It is thus possible to avoid the micro-chargingoperations of the battery and therefore to optimize the batteryperformances and life.

According to one particular embodiment, the smart card triggers saidrecharging upon receipt of said transaction command, only if the currentcharge level of the battery is below or equal to a predetermined minimumcharge level.

According to one particular embodiment, the transaction is a paymenttransaction of the type EMV, MONEO or GELDKARTE.

According to one particular embodiment, the transaction is an EMV-typetransaction, said predetermined transaction command being one among thefollowing APDU commands within the meaning of the EMV standard: GPO, GACand VERIFY PIN.

According to one particular embodiment, the transaction is a MONEO-typetransaction, said predetermined transaction command being one among thefollowing APDU commands: DEBIT, DEBIT REVERSAL and VERIFY PIN;

According to one particular embodiment, the transaction is aGELDKARTE-type transaction, said predetermined transaction command beingone among the following APDU commands: DEBIT and REPAYMENT.

According to one particular embodiment, the method further comprisesstopping the recharging of the battery upon detecting that the chargelevel of the battery has reached a second predetermined threshold chargelevel. This second threshold charge level is greater than or equal tothe first threshold recharge level.

According to one particular embodiment, the power supply is received,from the external terminal, by external contact.

According to one particular embodiment, the smart card is of the typeISO 7816, the power supply being received, from the terminal, by contactvia the contact Vcc connected to the external terminal.

According to one particular embodiment, the smart card triggers therecharging of the battery, simultaneously by contact and withoutcontact, from the external terminal.

According to one particular embodiment, the method further comprises,prior to said triggering of the recharging of the battery: upondetecting that the charge level of the battery is below a thirdthreshold charge level, sending to the external terminal a first commandrequiring that the transaction is processed by contact.

According to one particular embodiment, the method further comprises,prior to said triggering of the recharging of the battery: upondetecting that the charge level of the battery is below the thirdthreshold charge level, sending a second command to a user interface ofthe smart card to create the presentation to a user of a notificationindicating that the transaction must be processed by contact.

According to one particular embodiment, the method further comprises:sending to the external terminal a timing command requiring that theexternal terminal artificially extends a processing time necessary tocarry out a processing during said transaction, so as to allow carryingout said recharging of the battery.

According to one particular embodiment, the transaction is of the EMVtype, the timing command requiring the extension of a processing timeused by said external terminal to perform a processing within the limitsauthorized by the EMV standard.

According to one particular embodiment, the smart card comprises anon-rechargeable cell, the method further comprising: upon detectingthat the charge level of the battery is below a fourth threshold chargelevel, triggering the recharging of the battery from the cell tosupplement or complement the power supply delivered by the externalterminal. The fourth threshold charge level is for example below orequal to the first threshold charge level.

According to one particular embodiment, upon detecting that the chargelevel of the battery increases until reaching a fifth threshold chargelevel, interrupting the recharging of the battery by the cell so thatthe recharging of the battery continues only from the power supplydelivered by the external terminal. The smart card can thus switch backonly to the supply of the terminal in order to preserve the internalcell of the smart card and thus extend its lifetime.

In one particular embodiment, the different steps of the control methodare determined by computer program instructions.

Consequently, the invention also aims a computer program on aninformation medium (or recording medium), this program being likely tobe implemented in a smart card, or more generally in a computer, thisprogram including instructions adapted to the implementation of thesteps of a control method as defined in this document.

This program can use any programming language, and be in the form ofsource code, object code, or intermediate code between source code andobject code, such as in a partially compiled form, or in any otherdesirable form.

The invention also aims a computer-readable information medium (orrecording medium), and including instructions of a computer program asmentioned above.

The information medium may be any entity or device capable of storingthe program. For example, the medium may include a storage means, suchas a ROM, for example a CD ROM or a microelectronic circuit ROM, or amagnetic recording means, for example a floppy disc or a hard disk.

On the other hand, the information medium may be a transmissible mediumsuch as an electrical or optical signal, which may be conveyed via anelectrical or optical cable, by radio or by other means. The programaccording to the invention can be particularly downloaded on an Internettype network.

Alternatively, the information medium may be an integrated circuit inwhich the program is incorporated, the circuit being adapted to executeor to be used in the execution of the method in question.

The invention also aims a corresponding smart card. More particularly,the invention relates to a smart card comprising:

-   -   a rechargeable battery;    -   a processing module configured to process a transaction during        which the smart card communicates with an external terminal with        which said smart card is coupled;    -   a communication module configured to receive, during said        processing of the transaction, a predetermined transaction        command requiring a processing time, by said smart card, long        enough to allow a recharging of the battery to at least a first        predetermined threshold charge level; and    -   a control module configured, upon detecting that said        predetermined transaction command is received, to trigger the        recharging of the battery by using a power supply delivered by        the external terminal in order to reach at least the first        predetermined threshold charge level.

Note that the various embodiments mentioned in this document in relationto the control method of the invention as well as the associatedadvantages apply in a similar manner to the smart card of the invention.For each step of the control method of the invention, the smart card ofthe invention may comprise a corresponding module configured to performsaid step.

According to one embodiment, the invention is implemented by means ofsoftware and/or hardware components. In this context, the term “module”may correspond in this document both to a software component and to ahardware component or to a set of hardware and software components.

A software component corresponds to one or several computer programs,one or several subroutines of a program, or more generally to anyelement of a program or software able to implement a function or a setof functions, according to what is described in this document for themodule concerned.

In the same way, a hardware component corresponds to any element of ahardware set able to implement a function or a set of functions,according to what is described in this document for the moduleconcerned. It can be a programmable hardware component or with anintegrated processor for running the software.

SHORT DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the present invention willappear from the description given below, with reference to the appendeddrawings which illustrate therefrom examples of embodiment withoutlimitation. In the figures:

FIG. 1 schematically represents the change in the charge level of abattery during successive recharge cycles;

FIG. 2 is a diagram generally describing the processing of a transactionaccording to the EMV protocol;

FIG. 3 schematically represents an environment comprising a smart cardaccording to one particular embodiment of the invention;

FIG. 4 schematically represents the functional modules implemented by asmart card according to one particular embodiment of the invention;

FIG. 5A represents, in the form of a diagram, the steps of a controlmethod according to one particular embodiment of the invention;

FIG. 5B schematically represents a control method according to oneparticular embodiment;

FIG. 6 represents, in the form of a flowchart, the steps of a controlmethod according to one particular embodiment of the invention;

FIG. 7 represents, in the form of a flowchart, the steps of a controlmethod according to one particular embodiment of the invention; and

FIG. 8 represents, in the form of a flowchart, the steps of a controlmethod according to one particular embodiment of the invention.

DETAILED DESCRIPTION OF SEVERAL EMBODIMENTS

As indicated above, the invention relates to the management of the powersupply in a smart card (also called “microcircuit card”) embedding arechargeable battery, and relates more particularly to the electricalrecharging of such an embedded battery.

The invention proposes to optimize the electrical recharging process ofan internal battery with which a smart card is equipped.

The invention, according to various embodiments, relates to a controlmethod implemented by a smart card embedding at least one rechargeablebattery. The smart card can process a transaction with an externalterminal and, upon detection of a predetermined transaction commandcoming from the external terminal, the smart card is configured totrigger the recharging of the battery by using a power supply deliveredby the external terminal.

Particularly, the invention aims a control method implemented by a smartcard including a rechargeable battery, the method comprising: aprocessing of a transaction during which the smart card communicateswith an external terminal with which said smart card is coupled;receiving, during said processing of the transaction, a predeterminedtransaction command requiring a processing time, by said smart card,long enough to allow a recharging of the battery to at least a firstpredetermined threshold charge level; and, upon detection of saidpredetermined transaction command, triggering the recharging of thebattery by using a power supply provided by the external terminal toreach at least the first predetermined threshold charge level.

As explained below, the invention allows implementing an intelligentelectrical recharging of the battery. The smart card is indeed capablefor controlling the recharging of the battery, from the supply deliveredby the external terminal, at the most appropriate moment during thecurrent transaction, that is to say the moment offering the bestconditions of stability of the power supply as well as a limited riskthat the recharging will be interrupted early, before completion of therecharging process. To do so, the smart card of the invention triggersthe recharging upon detection of a predefined transaction command, whichallows choosing an optimal period of time in the course of thetransaction to perform the recharging. Thanks to the invention, thephase of the transaction during which the recharging is performed isselected so as to ensure a certain stability of the power supply for atime sufficient to the embedded battery to reach a desired charge level,and this by limiting the risks of an unexpected interruption of therecharging process.

The invention also aims the corresponding smart card, as well as thecorresponding computer program.

Other aspects and advantages of the present invention will appear fromthe examples of embodiment described below with reference to thedrawings mentioned above.

In this document, examples of implementation of the invention aredescribed within the context of a smart card in accordance with the ISO7816 standard, although other implementations are possible.

Likewise, a smart card in accordance with the EMV standard issubsequently considered. As indicated in more detail later, however, itwill be understood that the invention does not apply exclusively to theEMV standard but may apply to other protocols, such as MONEO™ orGELDKARTE™ payment protocols, for example.

EMV is the standardized protocol used today mainly in the world tosecure in particular the payment transactions made by smart cards.

The EMV protocol has been designed to reduce the risks of frauds duringa payment transaction by allowing in particular the authentication ofboth the smart card and its holder. This authentication process uses acombination of cryptograms (or encrypted keys) and digital signaturesand requires possibly the entry of a secret code (commonly called PINcode) by the cardholder.

Depending on the type of smart card used, the situation, or the amountconsidered, an EMV card can work online or offline. In online mode, theEMV card communicates, via the reader, with a remote server (a server ofthe card-issuing bank, for example) in order to verify the validity ofthe current transaction. However, if the EMV card is operates in offlinemode, it applies prerecorded verification criteria to decide whether thetransaction should be authorized or refused.

Unless otherwise indicated, the elements common or similar to severalfigures bear the same reference signs and have identical or similarcharacteristics so that, for the sake of simplicity, these commonelements are generally not described again.

The notion of transaction is here understood in a broad sense andcomprises, for example, in the banking field, both a payment or transfertransaction and a consultation of a bank account on a bank terminal. Theinvention is described here as part of a payment card intended to carryout banking transactions according to the EMV protocol. It will beunderstood that other types of transactions or operations areconceivable within the context of the invention.

In order to facilitate the understanding of the invention, an example ofa processing of a transaction in accordance with the EMV protocol,carried out by a smart card 100 in cooperation with an external terminal(or reader) 110, is described now with reference to FIG. 1. The terminal2 is able to communicate with a bank server 120 associated with theissuer of the smart card 100. In this example, the smart card 100 is apayment card and the reader 110 is a payment terminal.

As indicated below, the smart card 100 operates here in a mode withverification of the secret code (PIN code) although it is possible toconsider variants according to which the smart card 100 does not proceedto the verification of the secret code (mode without verification of thesecret code).

A payment EMV smart card can contain different banking applications,allowing for example to operate in “credit card” or “debit card” mode ina point-of-sale or to interact with an automated teller machine.

It is assumed here that the holder inserts the smart card 100 in theterminal 110 or initiates a contactless transaction, denoted TR0, bypresenting the smart card 100 in the vicinity of the terminal 110.

The EMV protocol comprises a preliminary PHP phase intended to preparethe smart card 100 and the reader 110 for the implementation of thetransaction TR0. Different transaction messages in accordance with theEMV protocol are exchanged between the smart card 100, the terminal 110and (in this example) the bank server 120 during the transaction TR0.

More specifically, during the preliminary phase PHP, the terminal 110transmits (E2) a RESET message (RST) to the payment card 100. The latterresponds (E4) thereto by an ANSWER TO RESET message (ATR).

The receipt of the command RST (E2), by the smart card, marks thebeginning of the EMV transaction.

The terminal 110 then tries to choose the appropriate application on thepayment card 100. To do so, the terminal 110 sends (E6) to the smartcard 100 a SELECT FILE command in order to ask the smart card for theapplications that the latter is able to execute. In response, the smartcard 100 transmits (E8) to the reader 2 a list of the differentapplications that it can implement. The holder can then select via theterminal 110 the desired transaction mode, thus triggering the sending(E10) to the smart card 100 of a SELECT APPLICATION command with theidentifier of the selected application as parameter.

The terminal 110 then sends (E10) a GET PROCESSING OPTIONS (GPO)command, well known to those skilled in the art, to the smart card 100.

In response, the smart card 100 sends (E14) to the terminal 110 a firstseries of information, such as the AIP (Application Interchange Profile)which indicates to the terminal 110 the different operations to becarried out to complete the transaction. The card 100 also sends (E16)an AFL (Application File Locator) message which indicates the list ofdata available at the application in the smart card 100 and that theterminal 110 must read to be able to carry out the transaction TR0. Theterminal 110 reads (E18-E20) thus the information specified in the AFL.To do so, the terminal 110 sends (E18) one or several READ RECORD readcommands to the smart card 100 and receives back (E20) the requestedinformation (called RECORDS).

The information read (E18-E20) by the terminal 110 in the smart card 100comprise for example the expiration date of the smart card 100, theassociated account number, a digital signature to authenticate the card100, control parameters to be used thereafter to perform thetransaction, and/or lists of objects called CDOL lists (Card Data ObjectList).

Various embodiments can be considered. In this example, the terminal 110performs (E22) then an analysis step from the information provided (E20)by the smart card 100. If the authentication associated with the smartcard 100 fails, if an anomaly is detected or if too much risk isdetected, the terminal 110 may refuse the transaction. It is assumedhere that the analysis E22 was made successfully.

The processing of the transaction TR0 according to the EMV protocolcontinues with an authentication phase of the holder of the smart card100 according to one of the methods listed and supported by said card.The terminal 110 determines the holder authentication method to beapplied based on the information previously received in the controlparameters. This phase allows particularly the terminal 110 to determinewhether the transaction is performed in a mode with verification of thePIN code or in a mode without verification of the PIN code.

In this example, where the mode with verification of the PIN code isimplemented, the holder is invited to enter his PIN code using thekeyboard with which the terminal 110 is generally provided. The terminal110 sends (E24) then to the smart card 100 a VERIFY PIN request forverifying the PIN code entered by the holder. The smart card 100compares (E26) then the PIN entered by the holder with a reference PINcode stored in its memory and deduces therefrom whether the holder isauthentic or not.

If the entered PIN code is valid, the smart card 100 transmits (E28) apositive authentication message OK to the terminal. Otherwise, the cardsends (E28) a refusal message to the terminal 110. There is here aninterest only for the case of an offline PIN code verification that isto say without the terminal 110 using the smart card issuer in the PINcode verification process, although this is also possible.

Once the holder is authenticated, the EMV protocol continues with averification phase of the transaction TR0. More specifically, theterminal 110 generates and then sends (E30) to the smart card 100 a GACcommand (GENERATE AC or Generate Application Cryptogram) well known tothose skilled in the art. This GAC command may comprise various datapreviously requested by the smart card 100. Typically, the GAC commandcontains information such as at least one among the amount of thecurrent transaction, the currency used, the type of transaction, etc.

In response to the GAC command, the smart card 100 performs (E32) ananalysis step, also called CRM (Card Risk Management), comprisingcertain predetermined security verifications. The number and the natureof these verifications are not standardized by the EMV protocol and mayvary from case to case.

At the end of the analysis E32, the smart card 100 responds to theterminal 110 by sending (E34) a cryptogram (or cryptographiccertificate). The response of the card depends in particular on thesetting of the card 100 made by the issuing bank.

In this example, the smart card 100 transmits (E34) an ARQC cryptogram(Authorization Request Cryptogram) indicating that the smart card wishesto continue the online transaction with the bank server 120 of theissuer of the card. The online processing of an EMV transaction allows aremote server (here the bank server 120) to perform complementaryverifications.

The terminal 110 thus transmits (E36) the ARQC cryptogram to the bankserver 120 at which an analysis is made (E38) from the receivedinformation. This analysis E38 typically comprises a number ofverifications to ensure that the transaction is valid. The terminal 110receives (E40) in response an encrypted ARPC message indicating thedecision of the issuer. The terminal 110 transmits (E42) this ARPCmessage to the payment card 100 in order to indicate thereto thedecision taken by the issuer.

If the smart card 100 accepts the transaction, the latter sends (E44) inresponse a TC (accepted transaction) type cryptogram to the terminal110. Otherwise, the smart card 100 sends (E44) an AAC-type cryptogramindicating the refusal of the transaction.

The messages exchanged according to the EMV protocol, in particularbetween the smart card 100 and the terminal 110, constitute transactionmessages intended to allow the processing of a transaction by the smartcard 100 in cooperation with the terminal 110.

It should be recalled here that the progress of the EMV protocoldescribed above with reference to FIG. 2 constitutes only a non-limitingexample. The EMV protocol offers indeed many alternatives. It is up tothe integrators to make the necessary choices to adapt the execution ofthe protocol as needed (holder authentication method, online or offlinetransaction, etc.).

With reference to FIG. 3, a smart card CD1 is now described according toone particular embodiment of the invention. In this example, the smartcard CD1 is a payment card (or bank card) configured to process paymenttransactions according to the EMV protocol. As already indicated, othertypes of protocols and other types of transactions are however possiblewithin the context of the invention.

The smart card CD1 is configured to cooperate with an external terminalT to perform EMV transactions. The external terminal T can interfacebetween the smart card CD1 and a remote server SV managed by the issuerIS of the smart card CD1.

In this example, the smart card CD1 comprises external contacts 2 inaccordance with the ISO 7816 standard to cooperate by contact with theexternal terminal T. It is assumed here that the smart card CD1 can alsocommunicate with the terminal T in contactless mode, by using an RFantenna 20 which is also possibly embedded in the smart card CD1,although this is not mandatory. The invention applies to the smart cardsconfigured to operate only by contact, to the smart cards configured tooperate only in contactless mode and to the smart cards configured tooperate in contact mode and in contactless mode (cards smart with dualcommunication interfaces).

The smart card CD1 further comprises a first processor 4, a non-volatilememory 5, a second processor 6, a rechargeable battery 8 and possibly atleast one additional component such as a sensor 10 (a biometric sensorfor example) and/or a user interface 12. In this example, the userinterface comprises for example at least one light-emitting diode (LED)14 and/or one screen 16, of the electronic paper (or “e-paper”) type forexample. Other configurations are however possible.

The nature and the number of these additional components may vary fromcase to case. Each of these additional components may be electricallypowered by the battery 8. Optionally, the smart card CD1 may alsocomprise a (non-rechargeable) cell 18 configured to recharge the batteryand/or to power the additional components as an alternative powersource.

The first processor 4 controls the other internal components of thesmart card CD1 by using in particular its non-volatile memory 5 and arandom access memory (not represented).

The memory 5 is a rewritable non-volatile memory or a read only memory(ROM), this memory constituting a recording medium (or informationmedium) according to one particular embodiment, readable by the smartcard CD1, and on which a computer program PG1 is recorded according toone particular embodiment. This computer program PG1 includesinstructions for performing the steps of a control method according toone particular embodiment. Examples of implementation of this method aredescribed in more detail later with reference to the figures.

The second processor 6 is in this example an EMV processor configured toprocess transactions according to the EMV protocol.

The internal battery 8 (also called “accumulator battery”) includes in awell-known manner a plurality of electrical accumulators (or cells)connected together so as to form an electric voltage generator.

Various types of battery can be considered within the context of theinvention, insofar as this battery can be sufficiently compact to beembedded in a smart card. The battery 8 may be in particular accordingto any of the following types: Lithium-ion, Lithium-Polymer,super-capacitor . . . .

At least one super-capacitor (or super-capacitance) can further beembedded in the smart card CD1 to collect the power supply deliveredduring a recharging and transmit it later gradually to the battery 8.The smart card CD1 can thus implement a mechanism involving asuper-capacitor to recover energy from the external terminal T for ashort time, the collected energy being used later to recharge thebattery. In this case, the method of the invention allows recharging theembedded super-capacitor at an appropriate moment during a transaction,with a view to using subsequently this super-capacitor in order torecharge the battery 8. It can also be considered that the smart cardCD1 comprises in this case a battery system comprising the battery 8 andthe super-capacitor, this battery system being rechargeable according tothe principle of the invention.

The smart card can be configured to use the RF antenna 20 (if the latterpresent in the smart card) to cooperate in contactless mode with theterminal T. The RF antenna 20 can be configured to collect inductivelyelectrical energy to electrically power the battery 8. As explainedbelow, the RF antenna 20 can thus be used to recharge at least part ofthe battery 8 from the terminal T.

It will be understood that certain elements generally present in a smartcard have been deliberately omitted because they are not necessary tounderstand the present invention.

It should also be noted that the smart card CD1 represented in FIG. 3constitutes only one example of embodiment, other implementations beingpossible within the context of the invention. Those skilled in the artunderstand particularly that certain elements of the smart card CD1 aredescribed here only to facilitate understanding of the invention, theseelements are not necessary to implement the invention.

The first processor 4 driven by the computer program PG1 here implementsa number of modules represented in FIG. 4, namely: a processing moduleMD2, a communication module MD4 and a control module MD6.

The processing module MD2 is configured to process a transaction (of theEMV type in this example) during which the smart card CD1 communicateswith the external terminal T with which the smart card is coupled. Inthe example considered here, the processing module 4 is implemented byboth the first processor 4 and the second processor 6.

The communication module MD4 is configured to receive, during theprocessing of a transaction by the processing module MD2, apredetermined transaction command coming from the external terminal T.The receipt of this predetermined transaction command indicates to thesmart card CD1 the starting of a time range, in the transaction, whichis particularly suitable for carrying out the electric recharging of thebattery 8.

In one particular example, the communication module MD4 is configured todetect that this predetermined transaction command is such that itrequires a processing time, by the smart card CD1, which is long enoughto allow a recharging of the battery (by the external terminal T) untilreaching at least a first predetermined threshold charge level (denotedhereinafter TH1). This processing time may be inherent to thespecifications of the EMV standard and/or to the configuration of thesmart card CD1.

As indicated below, the first predetermined threshold charge level ischosen large enough to avoid the above-described phenomena ofmicro-recharging which are detrimental to the battery performances andlife. According to one particular embodiment, this first predeterminedthreshold charge level corresponds to 50%, or even 55% or 60%, of themaximum charge capacity (nominal charge capacity) of the battery.

The control module MD6 is configured, in response to said predeterminedtransaction command received by the communication module MD4, to triggerthe recharging of the battery 8 by using a power supply delivered by theexternal terminal T. The recharging can thus be performed until reachingat least the first predetermined threshold charge level.

As indicated below, the predetermined transaction command mentionedabove may be suitably chosen by those skilled in the art to trigger therecharging of the battery 8 at a stage of the current EMV transactionoffering adequate conditions in particular in terms of stability of thepower supply and of duration during which the power supply can bemaintained without interruption. There is a risk that the currenttransaction ends early, due in particular to a problem occurring duringthe transaction or because the user decides to unexpectedly interruptthe transaction (for example, by uncoupling the smart card from theterminal), thus causing at the same time the end of the recharging. Thisrisk can be limited by choosing, in order to carry out the recharging, astage of the transaction where it is unlikely that the transaction ends.The recharging process can also be improved by choosing as a rechargeperiod, a part of the transaction ensuring the stability of the powersupply delivered by the external terminal T.

The configuration and the operation of the modules MD2-MD6 of the smartcard CD1 will appear more precisely in the examples of embodimentdescribed hereinafter with reference to the figures. It is understoodthat the modules MD2-M6 as represented in FIG. 4 represent only onenon-limiting example of implementation of the invention.

One particular embodiment of the invention is now described withreference to FIGS. 5A and 5B. More specifically, the smart card CD1described above with reference to FIGS. 3-4 implements, in cooperationwith the terminal T, a control method by executing the computer programPG1.

It is assumed that the user UR (FIG. 3) initiates an EMV transaction bycooperating by contact the smart card CD1 with the external terminal T.To do so, the user UR inserts the smart card CD1 into the terminal Ttaking here the form of a payment terminal.

During a step S30, the smart card CD1 detects the initiation of anEMV-type transaction TR1. The smart card CD1 can, for example, detectthe initiation of the transaction TR1 upon receipt of the transactionmessage RST in accordance with the EMV standard (as already describedwith reference to FIG. 2, step E2), coming from the terminal T.

The smart card CD1 then processes (S30) the transaction TR1 according tothe EMV protocol. To this end, the smart card CD1 is coupled with theexternal terminal T. In this example, this coupling results incontacting the external contacts 2 of the smart card CD1 with theexternal terminal T. This coupling is represented by the reference L1 inFIG. 3.

During the processing of the transaction TR1, the smart card CD1communicates (S30) by contact with the terminal T with which it iscoupled. According to another example, it is also possible tocommunicate the smart card CD1 in contactless mode with the terminal T.

During the processing (S30) of the transaction TR1, the smart card CD1verifies (S32) if it detects a predetermined transaction command CMD1coming from the external terminal.

The transaction command CMD1 is predefined so that it indicates to thesmart card CD1 the beginning of a period of time, during the processingof the EMV transaction TR1, during which it is appropriate to carry outthe recharging of the battery 8.

In this example, the predetermined transaction command CMD1 requires aprocessing time long enough to allow a recharging of the battery up toat least a first predetermined threshold charge level TH1. As indicatedbelow, the period during which this processing is carried out in thetransaction offers favorable stability conditions of the power supplydelivered by the terminal T.

The predetermined threshold charge level TH1 corresponds for example toat least 50% of the maximum charge capacity of the battery. For example,TH1 is equal to 50% or even 55% or 60% of the maximum charge capacity ofthe battery 8. This charge level TH1 is chosen so that the rechargingcan be triggered over a relatively short period of time within thecontext of the processing of a current transaction, while avoiding tooshort recharge phases (micro-recharging operations), harmful to thebattery 8 performances and life.

In response to the predetermined transaction command CMD1 received (S32)coming from the terminal T, the smart card CD1 triggers (S34) theelectrical recharging of the battery 8 by using a power supply deliveredby the external terminal T. The smart card is thus capable of carryingout the recharging (S34) of the battery, from the external terminal, atthe most appropriate moment of the transaction TR1.

According to the example described here, the predetermined transactioncommand CMD1 is not the RST message in accordance with the EMV standard,the command CMD1 being received after the RST message. The triggering ofthe recharging of the battery 8 is thus delayed relative to thebeginning of the EMV transaction, in order to wait for a more favorableperiod of processing offering satisfactory stability conditionsconcerning the power supply provided by the external terminal.

FIG. 5B illustrates for example a first case where the smart card CD1detects in S32 that the command CMD1 is received and that its processingtime is long enough to recharge the battery from its current chargelevel, noted NC1, up to at least the predetermined threshold chargelevel TH1. The recharging can continue as long as the smart card CD1 isnot uncoupled from the terminal T, until reaching where necessary thelevel TH2 as described below.

According to one particular example, when a transaction command CMD1 isreceived at S32 (FIG. 5A), the smart card CD1 determines, from thecurrent charge level NC of the battery 8, whether the processing time ofthis transaction is sufficient to allow a recharging of the battery 8 atleast up to the predetermined threshold charge level TH1. The methodcontinues in step S34 only if it is the case. In other words, inresponse to the detection that a transaction command CMD1 receivedrequires a processing time, by the smart card CD1, sufficient to allow arecharging of the battery 8 at least up to the predetermined thresholdcharge level TH1, the smart card CD1 proceeds to the triggering step S34as already described. Indeed, the recharge time to reach at least thislevel TH1 may vary depending on the current charge level of the battery.A given period of a current transaction may therefore be favorable toinitiating the recharging of the battery only when the current chargelevel NC is in a certain range for example.

In one particular example, the smart card CD1 also verifies at S32 (FIG.5A) whether the charge level NC is below a predetermined minimum chargelevel THmin. The smart card CD1 then triggers at S34 (FIG. 5A) theelectrical recharging of the battery 8 only if the two followingconditions are met:

-   -   a) receipt of a predetermined transaction command CMD1, this        command requiring a processing time by the smart card CD1 which        is long enough to allow a recharging of the battery 8 up to at        least the first predetermined threshold charge level TH1; and    -   b) the current charge level NC is below or equal to the        predetermined minimum charge level THmin (THmin≤TH1).

In other words, according to this particular example, THmin defines athreshold value of the current charge level NC above which the smartcard CD1 does not trigger the recharging of the battery 8. This allowsthe smart card CD1 to avoid triggering a recharging of the battery 8unnecessarily if its current charge level NC is too close to its maximumcharge capacity, so as to further reduce the risks of micro-rechargingand preserve the battery life as much as possible.

In one particular example, the value THmin is set so that the difference(TH1-Thmin) represents at least 10%, or even 15% or 20%, of the maximumcharge capacity of the battery.

FIG. 5B illustrates for example a second case where the smart card CD1receives the command CMD1 and triggers the recharging of the battery 8upon detecting that the current charge level, noted NC2, of the battery8 is below or equal to the predetermined minimum charge level THmin andthat the processing time of the command CMD1 is long enough to allow therecharging of the battery 8 from the current charge level NC2 up to atleast the threshold charge level TH1.

Generally, to determine at S32 (FIG. 5A) whether a received commandrequires a processing by the smart card CD1 long enough to recharge thebattery 8 up to at least the charge level TH1, the smart card CD1 mayfor example determine from the current charge level NC a recharge timerequired to reach at least the charge level TH1 by using the powersupply of the terminal T and can then compare this estimated rechargetime with a reference processing time required for the processing of thereceived command. The smart card CD1 triggers (S34, FIG. 5A) then therecharging of the battery 8 only if the reference processing time isgreater than or equal to the estimated recharge time.

With reference to FIG. 5B, T1 denotes for example the time required torecharge the battery 8 from the predetermined minimum charge level THminup to the first predetermined charge level TH1. According to oneparticular example, T1 thus corresponds to the minimum recharge timerequired to carry out a recharging by using the power supply deliveredby the terminal T (in the case where the condition b) mentioned above isapplied). The smart card CD1 can then verify at S32 (FIG. 5A) whetherthe reference processing time required to process the received commandexceeds the time T1. From this time T1, it is thus possible to predefinethe commands during a transaction that are likely to trigger arecharging of the battery 8.

Moreover, according to one particular example, the power supply of theexternal terminal T (FIG. 3) is delivered by contact via at least oneexternal contact 8 connected to the terminal T, for example via theexternal contact 8 corresponding to the contact Vcc within the meaningof the ISO 7816 standard. It is thus possible to provide in a fast andefficient manner the embedded battery 8 with a stable power supply,which allows optimizing the performances of the battery 8 and reducingthe recharge time.

According to one particular embodiment, during the recharging of thebattery 8, the smart card CD1 monitors the charge level of the batteryand verifies (S36) particularly whether a sufficient charge level isreached. In the example considered here, the smart card CD1 verifiesduring step S36 whether the battery 8 has reached a second predeterminedthreshold charge level TH2 (with TH2≥TH1). According to a particularexample, TH1=TH2. According to another example, TH2>TH1.

Upon detecting (S36) that this second charge level TH2 is reached, thesmart card CD1 causes stopping (S38) the recharging of the battery 8 byinterrupting the supply delivered by the terminal T. The smart card CD1can thus be configured so that the battery 8 is recharged to a desiredlevel TH2 which goes beyond the required minimum charge level TH1 (FIGS.5A-5B). This value TH2 may for example correspond to the maximum chargelevel (or maximum charge capacity) of the battery or to a level below itin order to avoid that the maximum charge level is reached, which couldreduce the battery life. The recharging of the battery 8 can thus bestopped after having completed a full or almost full recharge cycle. Bystopping the recharging once the threshold charge level TH2 is reached,stressing the battery 8 too much is avoided, which allows furtherextending its lifetime.

According to one particular example, the second threshold charge levelTH2 corresponds to 80%, or even 85% or 90%, of the maximum chargecapacity of the battery 8.

As already indicated, the invention makes it possible to implement anintelligent electrical recharging of the battery 8 by triggering therecharging at an appropriate moment in the current transaction TR1, soas to improve the performances of the battery 8. By triggering therecharging upon detection of the predefined transaction command CMD1, itis possible to choose a suitable period of time in the course of thetransaction TR1 to perform the recharging, which makes it possible inparticular to deliver a stable supply for a time sufficient to thebattery 8 until at least a first desired charge level is reached.

The power supply delivered by the external terminal T may indeed bedisturbed or even interrupted, while the battery 8 is still beingrecharged. The transaction TR1 can for example stop early because of aproblem occurring during the transaction (coupling problem, refusal ofthe smart card to process the transaction, . . . ) or due to anunexpected stop of the transaction by the user that uncouples the smartcard CD1 of the terminal T while the transaction is not completed.

The instability of the power supply or the unexpected interruption ofthe recharging process during a recharge phase can cause the acceleratedaging of the battery and reduce its performances. By controlling thesmart card so that is ensures the recharging of the battery for anadequate period of the EMV processing, the battery life and performancescan be advantageously improved.

According to the invention, the smart card CD1 verifies whether apredetermined transaction command CMD1 is received, this commandrequiring a processing time, by the smart card, long enough to allow arecharging of the battery 8 to at least a first predetermined thresholdcharge level TH1. This assumes that the period during which the smartcard CD1 processes this command CMD1 offers power stability conditionswhich are favorable to recharging the battery at least up to the chargelevel TH1. For that, the processing command CMD1 must be chosenaccordingly. The processing of this command CMD1 for example makes earlyuncoupling of the smart card unlikely while the recharge phase of thebattery is still in progress, thus limiting the risks of a recharginginterruption already described above. This command can also be selectedbecause of the low risk that, during the processing of the command,disturbances are likely to affect the power supply delivered by theterminal T to recharge the battery 8.

The battery life can be further extended by making sure that arecharging is triggered only if its current charge level is below apredetermined minimum charge level, as previously described.

According to one particular embodiment, it is also possible to increasethe battery life by using a super-capacitor embedded in the smart cardto accumulate the energy of several transactions before recharging thebattery, for example once the accumulated energy reaches a predeterminedthreshold level. The recharging of the battery occurs for example offtransaction that is to say while the smart card is not coupled with anexternal terminal. This particular mode, it is therefore thesuper-capacitor that is recharged at the appropriate moment during theprocessing of the transaction in cooperation with the external terminal.According to one particular example, the smart card comprises a batterysystem comprising the rechargeable battery and said super-capacitor, thelatter being configured to accumulate energy during the rechargingprocess during transactions, in accordance with the principle of theinvention.

It is up to those skilled in the art to best choose the CMD1 transactioncommand marking the activation of the recharging of the battery 8, inparticular according to the specificities of the battery and of thesmart card, and also according to the implemented transaction protocol.This transaction command CMD1 must require a processing time, by thesmart card CD1, which is long enough to allow a recharging of thebattery to at least a first predetermined threshold charge level.Ideally, this processing time is subject to the fluctuations in thepower supply delivered by the external terminal. The recharging canfurther be triggered (S32-S34, FIG. 5A) during a period where nocomponent (processor or the like) of the smart card CD1, other than thebattery 8, has a power consumption that exceeds a predetermined level,in order to ensure a stable power supply to the battery coming from theexternal terminal.

In the example of embodiment described above, the predeterminedtransaction command CM1 can be one among the following APDU commandswithin the meaning of the EMV standard: GPO, GAC, and VERIFY PIN (asalready described above with reference to steps E12, E24 and E30 of FIG.2).

The GPO, GAC and VERIFY PIN commands each require relatively longprocessing of the smart card CD1, period during which there is little orno interaction with the terminal T. During the processing of thesepredetermined transaction commands, it has been determined that aminimum of disturbances is likely to negatively affect the recharging ofthe battery 8 by the external terminal T. Thus, each of the GPO, GAC andVERIFY PIN commands requires a processing time, by the smart card CD1,which is in accordance with the EMV standard and which is particularlylong enough to allow a recharging of the battery to at least the firstthreshold charge level TH1, from the power supply of the externalterminal T.

For example, recharging the battery 8 during the period during which theuser UR enters his PIN code on the external terminal T is advantageousin that there is little risk that the user UR terminates the transactionTR1 early by uncoupling for example the smart card CD1 and the terminalT. Also, it is advantageous to configure the smart card CD1 so that itcauses the recharging of the battery in response to the transactioncommand GPO coming from the terminal T.

For similar reasons, it is advantageous to cause the recharging of thebattery 8 in response to the detection, by the smart card CD1, of thetransaction command GPO or GAC.

The risk that the processing of the transaction TR1 stops early is forexample relatively high when establishing the coupling between the smartcard CD1 and the terminal T1, that is to say at the beginning of the EMVprotocol (exchange of the RST/ATR, steps E2-E4, FIG. 2) between thesmart card CD1 and the terminal T1. Thanks to the invention, therecharging of the battery is not triggered instantly as soon as thecoupling is achieved but later when the conditions for the rechargingare more favorable.

The invention is also advantageous in that it is not necessary to modifythe current transaction protocols (EMV in particular). The recharging ofthe battery 8 can be carried out in a transparent manner for the user URthat is to say without the latter noticing it or changing his habitssince the recharging process is integrated in an intelligent way in theEMV protocol, without significantly disturbing or slowing down thelatter.

In the example of embodiment described above with reference to FIG. 4,the transaction TR1 is processed according to the EMV protocol, althoughother implementations are possible. According to one particular example,the transaction TR1 is a payment transaction of the type EMV, MONEO(application purse) or GELDKARTE (application purse).

In one particular example, the transaction TR1 is carried out accordingto the EMV protocol defined by the specification “EMV Integrated CircuitCardSpecifications for PaymentSystems” (Book 3, ApplicationSpecification, Version 4.3 dating from November 2011).

According to one particular example, the transaction TR1 is carried outaccording to the MONEO protocol (electronic purse) defined by thespecification “ElectronicPURSE-MONEO-CardSpecification-PME-DSI9A-v2.5.2-22/01/2002-DSI9A Version2.5.2”.

In the case where the transaction TR1 is a MONEO-type transaction, thepredetermined transaction command CMD1 may be one among the followingAPDU commands: DEBIT (Instruction 0x34), DEBIT REVERSAL (Instruction0x36) and VERIFY PIN (Instruction 0x20).

According to one particular example, the transaction TR1 is carried outaccording to the GELDKARTE protocol defined by the specification“GeldKarteApplikationelektronischeGeldbörsefür SECCOS 6” (Version1.3-21/03/2011).

In the case where the transaction TR1 is a GELDKARTE-type transaction,the predetermined transaction command CMD1 can be one among thefollowing APDU commands: DEBIT (Instruction 0x34) and REPAYMENT(Instruction 0x36).

In the example of embodiment described above with reference to FIG. 4,the power supply of the external terminal T is delivered by contact, forexample via the external contact Vcc within the meaning of ISO 7816standard. According to another example, it is possible to configure thesmart card CD1 and the external terminal T for the latter to deliver tothe battery 8 a contactless power supply, for example by electromagneticinduction, using the RF antenna 20 of the smart card CD1. According toone particular example, the smart card CD1 triggers the recharging ofthe battery 8 by using the power supply delivered by the externalterminal T, both by contact (for example via the external contact 8 Vcc)and without contact (via the RF antenna 20). It is thus possible toaccelerate the recharging process of the battery 8 and to ensure thatthe desired number n of recharge cycles is reached without unexpectedinterruption of the recharging. This variant is particularlyadvantageous in the case of the terminals T (payment terminals or thelike) which are configured to emit RF signals even when communicationswith the smart card CD1 are made by contact.

According to another example of embodiment, the smart card DV1cooperates in contactless mode with the terminal T to process thetransaction TR1.

FIG. 6 represents an embodiment of the invention in which it is assumedthat the smart card CD1 cooperates in contactless mode with the externalterminal T to carry out the transaction TR1. In this example, thecommunication of the smart card CD1 with the terminal T is thus made byelectromagnetic coupling.

First, the smart card CD1 performs steps S30 and S32 as alreadydescribed above with reference in particular to FIGS. 3-4.

Once the predetermined transaction command CMD1 is detected (S32), thesmart card CD1 determines (S50) whether the current charge level-notedNC-of the battery 8 is below or equal to a third threshold value TH3. Ifthis is not the case, the smart card CD1 resumes the control method instep S34 as already described above.

If, on the other hand, the smart card CD1 detects (S50) that the currentcharge level NC of the battery 8 is such that: NC≤TH3, then the methodcontinues in step S52 during which the smart card CD1 performs at leastone predetermined action to force the processing by contact of thetransaction TR1.

This third threshold charge level TH3 can be chosen so that TH3≤TH1.

More precisely, during step S52 (FIG. 6), the smart card CD1 can performat least one of the following actions:

-   -   action S54 during which the smart card CD1 transmits to the        terminal T a command CMD2 requiring the processing by contact of        the transaction TR1;    -   action S56 during which the smart card CD1 transmits a command        CMD3 to its user interface 12 to create the presentation to the        user UR of a notification indicating that the current        transaction (or a subsequent transaction) must be processed by        contact.

Note that, according to one variant, the smart card CD1 can carry outthe detection step S50 before step S32.

The invention thus advantageously makes it possible to force theprocessing by contact when the battery 8 requires a recharging,especially when the current charge level is particularly low, in orderto be able to carry out the recharging by contact from the power supplyof the terminal T. Although a contactless recharging is possible in somecases (see below), a recharging by contact is generally faster andallows limiting the recharge time, which is important particularly whenthe current charge level is particularly low.

According to one variant, step S50 is not performed and the smart cardCD1 systematically performs step S52 represented in FIG. 6.

FIG. 7 represents one embodiment of the invention in which the smartcard CD1 performs steps S30 and S32 as already described above, thenperforms steps S60 and S62 in parallel with (or before or after) thetriggering S34 of the recharging the battery 8.

More precisely, upon detecting (S32) that the predetermined transactioncommand CMD1 is received, the smart card CD1 determines (S60) whetherthe current charge level-noted NC-of the battery 8 is below or equal toa fourth threshold value TH4. If this is the case (NC≤TH4), the smartcard CD1 proceeds to step S62 during which it sends to the externalterminal T a timing command CMD4 requiring that the terminal Tartificially extends a processing time necessary to achieve a processingduring the transaction TR1, so as to allow carrying out the rechargingof the battery 8.

This timing command CMD4 may in particular indicate to the terminal Tthe processing step (in accordance with the EMV protocol or the like)during which the terminal T must maximize its processing time.

The invention thus makes it possible to maximize the period, during theprocessing of the transaction TR1, during which the smart card CD1 islikely to cause the recharging (S36) of the battery 8. It is thuspossible to reach the threshold charge level TH1 (even beyond, untilpossibly reaching the charge level TH2) while limiting the risks thatthe recharging (S36) of the battery is interrupted before having reachedthe threshold charge level TH1. In other words, the invention makes itpossible to avoid any power supply cutoff delivered by the terminal Twhich could negatively affect the recharging of the battery.

The terminal T may for example be configured to reset and/or end thetransaction if it has no communication with the smart card CD1 during apredetermined period of inactivity, for example 1 second, which has theconsequence of uncoupling the smart card and cut off the power supplydelivered by the terminal T. To avoid such a power supply cutoff, thesmart card CD1 may require additional time to process the transactioncommand CMD1, by sending a timing command CMD4.

The timing command CMD4 requires, for example, the extension of aprocessing time used by the external terminal T to carry out aprocessing within the limits authorized by the EMV standard (or thelike).

The ISO 7816 defines in particular “PROCEDURE BYTE: 0x60” in the contactprotocol, this corresponds to a message that the card must sendregularly to the external terminal to inform it that it is alwayspresent (always coupled) and that it needs that the terminal allocatesadditional time thereto to complete its processing operations during thecurrent transaction. This command “PROCEDURE BYTE: 0x60” may constitutean example of timing command within the meaning of the invention. Forexample, between the receipt of a GAC command and the return of theresponse to this GAC command, the smart card can be configured to sendseveral “PROCEDURE BYTE: 0x60” commands (in T0) for the externalterminal to understand that it must wait for the response to the GACcommand.

The same principle can be applied within the context of the contactlessEMV protocol: it is thus possible to use the “WTX (WAITING TIMEEXTENSION)” command, well known to those skilled in the art.

The terminal T thus uses the maximum time authorized by thespecification of the EMV protocol (or the like) for the terminal toperform a step of processing the transaction, in order to extend theavailable processing duration to recharge the battery in optimalconditions.

According to one variant, the smart card CD1 proceeds to step S62without performing step S60. In other words, the smart card CD1systematically sends a timing command CMD4 regardless of the chargelevel of the battery 8.

FIG. 8 represents an embodiment of the invention in which the smart cardCD1 performs steps S30 and S32 as already described above, and thenperforms step S70. It is assumed here that the smart card CD1 includesthe cell 18 (FIG. 3).

More specifically, upon detecting (S32) that the predeterminedtransaction command CMD1 is received, the smart card CD1 determines(S70) whether the current charge level NC is below or equal to a fifththreshold value TH5. If this is not the case (NC>TH5), the smart cardCD1 continues the control method as already described above bytriggering (S36) the recharging of the battery 8 from the power supplydelivered by the terminal T.

If this is not the case (NC≤TH5), then the smart card CD1 proceeds tostep S36 as already described above and in parallel with step S72. Moreprecisely, in the case where the detection in S70 is positive (NC≤TH5),the smart card CD1 triggers (S36) the recharging of the battery 8 fromthe power supply delivered by the terminal T (by contact by example),and in parallel, triggers (S72) also the recharging of the battery 8 byusing the power supply provided by the internal cell 18.

The threshold charge level TH5 may be such that TH5≤TH1.

The cell 18 is thus used as a secondary power source to recharge thebattery, particularly when it has a very low charge level. By involvingthe cell 18, it is possible to reduce the recharge time of the battery,and thus to avoid slowing down excessively the processing of the currenttransaction TR1. The method thus makes it possible to recharge thebattery, even when it is almost or completely depleted, while allowingthe recharging process to be transparent to the user.

During step S72, the cell 18 can be activated to supplement (replace) orcomplement the power supply delivered by the terminal T.

According to one variant, the smart card CD1 systematically triggers(S72) the recharging of the battery 8 by the cell 18, as a complement tothe power supply delivered by the terminal T, regardless of the currentcharge level NC of the battery 8.

According to one variant, during the recharging (S72) by the cell, upondetecting that the current charge level NC of the battery 8 increasesuntil reaching a fourth threshold value, the smart card interrupts therecharging of the battery 8 by the cell so that the recharging of thebattery 8 continues only from the power supply delivered by the externalterminal T.

The invention thus allows ensuring that the battery 8 is recharged at asufficient charge level while preserving to the maximum the cell 18which is not rechargeable.

Those skilled in the art will understand that the embodiments andvariants described above constitute only non-limiting examples ofimplementation of the invention. Particularly, those skilled in the artmay consider any adaptation or combination of the embodiments andvariants described above in order to meet a particular need.

1. A control method implemented by a smart card including a battery thatis rechargeable, the method comprising: processing) a transaction duringwhich the smart card communicates with an external terminal with whichsaid smart card is coupled; receiving, during said processing of thetransaction, a predetermined transaction command; detecting, from acurrent charge level of the battery, that said predetermined transactioncommand requires a processing time, by said smart card, long enough toallow a recharging of the battery to at least a first predeterminedthreshold charge level; and in response to said detecting, triggeringthe recharging of the battery by using a power supply delivered by theexternal terminal to reach at least the first predetermined thresholdcharge level.
 2. The method according to claim 1, wherein the firstpredetermined threshold charge level corresponds to at least 50% of themaximum charge capacity of the battery.
 3. The method according to claim1, wherein the smart card triggers said recharging upon receipt of saidpredetermined transaction command-, only if the current charge level ofthe battery is below or equal to a predetermined minimum charge level.4. The method according to claim 1, wherein the transaction is anEMV-type transaction, said predetermined transaction command being oneamong the following APDU commands within the meaning of the EMVstandard: GPO; GAC; and VERIFY PIN.
 5. The method according to claim 3,wherein: the transaction is a MONEO-type transaction, said predeterminedtransaction command being one among the following APDU commands: DEBIT,DEBIT REVERSAL and VERIFY PIN; or the transaction is a GELDKARTE-typetransaction, said predetermined transaction command being one among thefollowing APDU commands: DEBIT and REPAYMENT.
 6. The method according toclaim 1, wherein the method further comprises: stopping the rechargingof the battery upon detecting that the charge level of the battery hasreached a second predetermined threshold charge level, greater than orequal to the first predetermined threshold charge level.
 7. The methodaccording to claim 1, wherein the power supply is received, from theexternal terminal, by external contact.
 8. The method according to claim7, wherein the smart card is of the type ISO 7816, the power supplybeing received, from the external terminal, by contact via a Vcc contactconnected to the external terminal.
 9. The method according to claim 7,wherein the smart card triggers the recharging of the battery,simultaneously by contact and without contact, from the externalterminal.
 10. The method according to claim 1, wherein the methodfurther comprises, prior to said triggering the recharging of thebattery: upon detecting that the charge level of the battery is below athird predetermined threshold charge level, sending to the externalterminal a first command requiring that the transaction is processed bycontact.
 11. The method according to claim 10, wherein the methodfurther comprises, prior to said triggering the recharging of thebattery: upon detecting that the charge level of the battery is belowthe third predetermined threshold charge level, sending a second commandto a user interface of the smart card to create a presentation to a userof a notification indicating that the transaction must be processed bycontact.
 12. The method according to claim 1, further comprising:sending to the external terminal a timing command requiring that theexternal terminal artificially extends a processing time necessary tocarry out a processing during said transaction, so as to allow carryingout said recharging of the battery.
 13. The method according to claim12, wherein the transaction is of the EMV type, and the timing commandrequiring the extension of a processing time used by said externalterminal to perform a processing within the limits authorized by the EMVstandard.
 14. The method according to claim 1, wherein the smart cardcomprises a non-rechargeable cell, the method further comprising: upondetecting that the charge level of the battery is below a fourthpredetermined threshold charge level, triggering the recharging of thebattery from the non-rechargeable cell to supplement or complement thepower supply delivered by the external terminal.
 15. A smart cardcomprising: a rechargeable battery; a processing module configured toprocess a transaction during which the smart card communicates with anexternal terminal with which said smart card is coupled; a communicationmodule configured to receive, during said processing of the transaction,a predetermined transaction command and to detect, from a current chargelevel of the battery, that said predetermined transaction commandrequires a processing time, by said smart card, long enough to allow arecharging of the battery to at least a first predetermined thresholdcharge level; and a control module configured, in response to saiddetection that the predetermined transaction command requires aprocessing time long enough to allow a recharging of the battery to atleast a first predetermined threshold charge level, to trigger therecharging of the battery by using a power supply delivered by theexternal terminal in order to reach at least the first predeterminedthreshold charge level.